The present invention relates to a fuel pump controller and, more particularly, to starting characteristics of an engine.
FIG. 5 shows a fuel pump driving system using a conventional fuel pump controller. Referring to FIG. 5, reference symbols E and F denote a battery and a fusible link, respectively, and reference numeral 1 denotes an ignition switch; 2, an ignition coil; 3, a point breaker connected in parallel with a capacitor 3a; 4, a fuel pump controller; and 5, a fuel pump circuit constituted by a blocking oscillator.
The fuel pump controller 4 includes a waveform shaping circuit WFT connected to a node N1 between the point breaker 3 and the primary side of the ignition coil 2 via a terminal T4, a one-shot circuit OC connected to the output terminal of the waveform shaping circuit WFT, a transistor TR to be turned on/off by an output from the one-shot circuit OC, and a diode D. When an ignition pulse is supplied to the terminal T4, the one-shot circuit 0C turns on the transistor TR for a predetermined time period to connect a power source on the side of a terminal T1 to the fuel pump circuit 5 via a terminal T2.
The fuel pump circuit 5 is constituted by a transistor 6, a biasing resistor 7 for the transistor 6, a signal coil 8, a main coil 9 for driving a fuel pump, diodes 10 to 12, and a varistor 13 serving as a surge absorber for absorbing a surge to protect the transistor 6. Blocking oscillation is caused by an electromagnetic tight coupling between the signal coil 8 and the main coil 9. A fuel pump (not shown) is driven by this blocking oscillation to supply fuel to an engine.
An operation of the conventional system having the above arrangement will be described below with reference to FIGS. 5 and 6A to 6C. As shown in FIG. 6A, the ignition switch 1 is switched on at a time t0. At this time, however, the fuel pump controller 4 does not supply a control current to the fuel pump circuit 5. When the engine is started at a time t1 as shown in FIG. 6C, an ignition pulse is generated at a primary coil of the ignition coil 2, i.e., the node N1 since the point breaker 3 which is turned on/off in accordance with engine rotation is turned off. When the ignition pulse is input to the terminal T4, the terminals T1 and T2 are electrically connected in the fuel pump controller 4 for a predetermined time period. That is, after the ignition pulse is subjected to waveform shaping processing performed by the waveform shaping circuit WFT, it triggers the one-shot circuit OC. Therefore, the one-shot circuit OC outputs a signal to the base of the transistor TR for a predetermined time period to turn on the transistor TR. In this manner, power is supplied from the battery E to the fuel pump circuit 5, and the fuel pump circuit 5 oscillates to drive the fuel pump.
In the fuel pump controller which operates as described above, if engine rotation is stopped at a time t2 (FIG. 6B) due to lateral turnover or crash of a vehicle and an ON/OFF operation of the point breaker is stopped, the ignition pulse is no longer generated to electrically disconnect the terminals T1 and T2, and the control current becomes zero as shown in FIG. 6C. Therefore, the fuel pump stops its operation and discharges no fuel. In this manner, safety for the fuel pump is assured.
In the above conventional fuel pump controller, supply of the control current to the fuel pump circuit 5 is controlled by the ignition pulse generated in accordance with engine rotation, and no control current is supplied to the fuel pump circuit 5 immediately after the ignition switch 1 is switched on.
For this reason, if a vehicle is a new one and left unused for a long time period or left at a high temperature under the blazing sun, the carburetor or piping may be emptied to degrade starting characteristics of an engine.